Particle replication

Recently it has been shown that hydrogel layers of variable thickness can be prepared on solid substrates by photolithographic technique [47], The technique called PRINT (particle replication in non-wetting templates) [48,49] utilizes elastomeric molds from a low surface energy perfluoropolyether network. The molds prevent the formation of an interconnecting film between molded objects and allow production of monodisperse microgel particles of different sizes, shapes, compositions, and surface functionalities. 

An important characteristic of heterogeneous polyethylene catalysts is the phenomenon of particle replication. Particle size distribution (psd) and morphology of the catalyst are reproduced in the polymer. If the catalyst is finely divided, the polymer will also be fine and may cause handling problems. If the catalyst contains agglomerates of oversized particles, so too will the polymer. Morphology replication is illustrated in Figure 3.2. Figure 3.3 shows how psd of the catalyst is mirrored in the polymer. 

Micromolding and PRINT (particle replication in nonwetting template) "lOOnm/medium [99,100]... 

A variant is the so-called technique that allows for the constmction of complete microstmctures by a roll-to-roll process [100]. Particle replication... 

MeBeInd)2ZrCl2-supported catalyst and the Novolen-BASF process. This catalyst can produce PP with high molecular weight even at elevated temperatures. The pol)nner particles replicate well the size distribution of the catalyst particles. This catalyst can produce PP with new properties, such as low extractables for food wrapping and medical applications, which is a consequence of the uniform stereoregularity of pol)maers produced with a single site-type catalyst. 

Microfabrication offers a way to produce homogeneous monodisperse particles that are not only spherical particles with controlled or asymmetrical shapes and architectures with a specific size can also be fabricated, which is not possible with the other methods. This method uses soft templates to produce monodisperse particles wherein the template can be fully dissolved in aqueous solutions once the particles are formed. There are many different methods of microfabrication particle replication in non wetting templates [72], microcontact hot printing [73], step and flash imprint lithography [74], and... 

The envelope glycoproteins of wild-type retroviruses and lentiviruses bind to cell surface receptors to facilitate entry of the vims into the cytoplasm where the viral RNA is reverse transcribed to form a cDNA, the proviras. This provirus is translocated to the nucleus where it integrates into the host cell chromosomes and through the normal process of DNA transcription encodes new viral proteins and new viral RNA, which are assembled at the cell surface into new viral particles. Replication-defective retroviral and lentiviral vectors infect cells by similar mechanisms, but unlike wild-type viruses, the integrated provirus from these vectors encodes the therapeutic gene and viral particles are not produced. 

---